Seasonal Uptake of Nutrients by Mature Field-grown 'Valencia' (Citrus sinensis 0.) Trees in California

摘要

Mature Campbell ' Valencia' orange (Citrus sinensis O.)trees at Lindcove Research and Extension Center in Tulare County, California, were sampled six times in a yearly cycle; winter 2003, bloom 2003, drop 2003, color break 2003, maturity 2004, and winter 2004. At each harvest date, entire trees were removed and partitioned into fruit, young leaves (ie, flushes) , mature leaves, small green branches, small brown branches, intermediate branches, large branches, trunk, large roots, medium roots, and fine roots. For the canopy, subsamples were taken and total weights of the individual organs estimated from total canopy mass. N uptake was estimated using the stable isotope N. There was not much seasonal variation in N concentration in most organs. In most organs, there appeared to be a slight increase in total N concentration at bloom. However, N concentrations in the leaves dropped at bloom. Flush N concentration was lower than expected. The increase in percentage total N in the permanent structure may have represented a mobilization of soil N, with it not yet arriving to the new growth or fruits. However, this does not appear to be the case based upon the estimation of the proportion of organ N being due to soil uptake. The bloom sampling represents the only significant seasonal change in total N concentration and so it is also possible that this sampling was anomalous for some unknown reason. Soil N was preferentially transported in the actively growing portions of the canopy, with lesser proportions going into the permanent structure. Soil not being transported into the trees from the soil would be supplied by the permanent structure via remobilization. Most of the macro- and micro-elements were assessed at each harvest. Both concentration and mass were significantly influenced by both sampling date and organ sampled, and in all except two cases, by the interaction of these factors. However, even statistically significant differences were not very large and probably do not have much physiological implication.